This invention relates generally to a process for providing a chrome finish onto substrates. Particularly, the invention relates to a process for vacuum metalizing chromium onto metal substrates. Specifically, this invention relates to a two step vacuum metalization process for chroming aluminum and steel substrates for automotive parts, for example, for providing a chrome layer on automatic parts such as vehicle wheels, hub caps, bumpers, and the like.
The metalization process of the present invention has specific and sequential steps to produce chromed aluminum and steel automotive parts having superior chrome adhesion characteristics to prevent delaminations and having chemical and road hazard resistant qualities. Although the disclosure herein discusses the process of metalizing chromium in the production of vehicle wheels, other chroming processes as well as the chroming of other metal substrates are within the purview of this invention.
In the past, aluminum and steel vehicle wheels, for example, have traditionally been electroplated to produce chrome wheels. These prior art processes require the wheel rim to be polished to provide a very smooth surface for the chrome plating to be effective. Further, the wheels are pretreated in hazardous chemicals to provide a clean and homogeneous surface for adherence of the chrome plating. The wheels are then coated with up to three different metal coatings with each step requiring the wheel to be submerged in hazardous solutions. The failure rate of these prior art processes is generally high. Additionally, should the chrome plated surface be damaged, corrosion or rust will typically begin rapidly, causing the chrome plating to delaminate from the wheel surface.
Another alternative prior art process has been developed which applies the chrome coating by vacuum metalization, thereby eliminating the application of the decorative coating using hazardous solutions. This prior art process entails applying one or two primer coat compositions to provide a smooth surface and to provide a suitable adhesion for the Cr to be applied. The wheel is then placed into a vacuum metalization chamber where a decorative coating is applied. Subsequently, a coating is applied to protect the metalized layer from environmental elements. The process produces chrome-like finishes on wheels, but not equal to the quality of the plating process and as such has not been accepted by the wheel manufacturers in the United States.
The present invention has overcome the difficulties and the shortcomings of the prior art. An object of the present invention is to provide a true chrome finish on wheels and the like that will be resistant to harsh climatic conditions. A further objective is to eliminate hazardous materials used during the application process and to greatly reduce the potential for delamination should the coating be damaged, impacted or scratched, as has been a problem with the prior art. This process is also applicable to any substrate where a durable, decorative, chrome finish is desired on automotive parts, for example, on vehicle wheels, bumpers, hub caps, and the like. Particularly, the object of the invention is to provide a vacuum metalization process for chroming metal substrates, such as aluminum and steel substrates.
The present invention relates to a process for chroming aluminum and steel substrates. The process of the invention utilizes a vacuum metalizing process which, preferably, comprises four stages: a cleaning or preparation stage utilizing a number of steps, a base coat application stage, a two-step Physical Vapor Deposition (PVD) stage, and a top coat application stage. Each stage utilizes specific process steps and uses particular formulations under specific process step parameters.
An aluminum or steel substrate or object, for example a vehicle wheel, to receive a decorative chrome coating is first cleaned to eliminate contamination. The cleaning stage begins by smoothing the wheel to provide a uniform surface roughness. Next, a series of washes are performed to the wheel; if the wheel is aluminum in composition, an alkaline/deionized water solution wash, followed by a deionized (DI) water rinse, followed by a non-Chromate/DI water solution coating, and finished with another DI water rinse. If the wheel is of a steel composition, the non-Chromate/DI water solution coating is replaced by an Iron Phosphate/city water solution conversion coating followed by a city water rinse. In the cleaning step for either the aluminum or steel composition, the wheel is rinsed with a final DI water rinse. The wheel is then dried using high-pressure filtered air and is subsequently placed in an oven to be outgassed. Last, the wheel is allowed to cool down.
The base coat applied in the base coat application stage is preferably an organic, thermosetting powder or the like and provides a smooth surface for Nickel/Chromium adhesion, however, an inorganic compound may be utilized. Alternatively, the base coat may be comprised of an electroplated coating, or e-coating. The wheel and base coat are heated to permit the coating to melt and flow evenly across the surfaces of the wheel. The temperature is then increased so that the organic powder will crosslink and solidify. The wheel temperature is then reduced in preparation for the two-step PVD stage.
To begin the two-step PVD stage, the wheel is placed into a PVD chamber to receive the chrome coating layer. The PVD stage consists of two steps. Both steps take place in vacuum conditions and by a sputtering or similar process, for example. The first step comprises sputtering an approximately 80% Nickel (Ni) and 20% Chromium (Cr) base metal layer onto the base coat on the wheel. The second step comprises sputtering an approximately 99.9% pure Chromium layer onto the metal base layer. As known in the art, various PVD and CVD processes are known utilizing metallic targets in vacuum conditions. Any such known processes may be utilized to deposit the Nickel/Chromium and Chromium layers according to the teachings of the invention.
The protective top coat applied in the topcoat application stage is preferably a clear, organic, thermosetting powder, although an inorganic compound and means to produce a colored finish may also be utilized. Alternatively, the top coat may be comprised of an electroplated coating, or e-coating. The top coat is applied to the wheel to cover the Chromium layer and is subsequently heated to cause crosslinking and solidification. The wheel is then permitted to cool down.
The vacuum metalization process of the present invention permits a decorative, chrome coating to be applied to a metal object, for example an aluminum or steel wheel, in an environmentally compatible manner without the use of hazardous chemicals and which is resistant to harsh climatic conditions and delamination. These and other benefits of this invention will become clear from the following description by reference to the drawings.